Low poly java terrian

I have a terrain that looks like this:enter image description here

(Don’t worry bout the textures or trees, I will fix that once I get the low poly going.) I’m trying to make it low poly and I know I could do it by generating a plane (like I’m doing now) but instead make it out of triangles. The problem here is obvious. I don’t know how to do this. I know this is a lot to ask but if anyone could help that would be great! heres the code.

[https://pastebin.com/QEXGAuvg][2]